Due to the close relationship between high cholesterol intake and the serum cholesterol level in humans (a factor in coronary heart disease), reduction in egg consumption, which is perhaps the largest single food source of cholesterol, has become a commonly accepted dietary measure in order to curb this ailment. Commercially available egg substitutes containing low or no cholesterol are thus becoming increasingly popular. These products are generally made of egg white with or without the yolk. To improve their palatability and stability, flavoring, coloring, emulsifying, thickening, and other modifying agents are generally added. Such products without the yolk are sold either frozen or refrigerated.
In the case of nonfrozen refrigerated products, liquid egg can be subjected to conventional pasteurization or ultra-pasteurization processes to extend its refrigerated shelf life. A typical time/temperature combination used for pasteurizing eggs is 3.5 minutes at 140.degree. F. During ultra-pasteurization processing, combinations of temperatures ranging from 147.degree. F. to a maximum of 162.degree. F. and holding times of 2.7 to 192 seconds have been reported (Journal of Food Science, Ball, et al., vol. 52, No. 5, 1987, p. 1212).
Certain protein fractions in egg heat denature at temperatures between 136.degree. F. and 144.degree. F. However, by using conditions of turbulent flow in a conventional heat exchanger, liquid egg can be heated to a maximum of 162.degree. F. with minimum protein denaturation. This is the theoretical foundation for ultra-pasteurization technology of eggs.
In the case of egg white, which is the high protein containing component of avian eggs and which is most sensitive to heat denaturation, ultra-pasteurization can only be carried out at temperatures below that used for whole egg. To reach the same processing temperature as whole egg (i.e. 162.degree. F.), added ingredients such as starch, oil, aluminum sulfate, and acid become necessary (see copending U.S. patent application Ser. No.).